1. Field of the Invention
The present invention relates to a sensor attachment structure of an actuator body for attaching, to a predetermined portion of the actuator body, a sensor for detecting a position of a movable section which is movable with respect to the actuator body under the action of an actuator.
2. Description of the Related Art
An electric actuator has been hitherto used, in which a workpiece or the like, which is installed to a movable section, can be moved back and forth in a reciprocating manner, for example, by transmitting the rotary driving force of an electric motor to the movable section by the aid of a feed screw shaft to allow the movable section to make linear reciprocating motion in the axial direction of an actuator body.
Such an electric actuator is incorporated, for example, into automated assembling steps and machining steps. It is necessary to automatically detect whether or not the electric actuator performs desired operation in a reliable manner. Therefore, a variety of sensors are usually attached to the actuator body which constitutes the electric actuator to make control so that the operation of the electric actuator is confirmed on the basis of the detection signal supplied from the sensor.
For example, as shown in FIG. 15, the electric actuator 1 comprises an electric motor 2 and an actuator body 3 which is connected to the electric motor 2. The electric actuator 1 is constructed such that a rod (movable section) 4 is movable back and forth in a reciprocating manner in the axial direction of the actuator body 3 (direction of the arrow A) under the driving action of the electric motor 2. In order to detect the reciprocating movement position of the rod 4, for example, the following structure is known. That is, an unillustrated magnet is installed to the rod 4, and a magnetism-detecting sensor (automatic switch) 5 is installed to a predetermined portion of the actuator body 3.
The magnetism-detecting sensor 5 is integrally composed of a main body section 5a having a substantially circular cross section, and a projection 5b having a substantially rectangular cross section. Sensor attachment grooves 6, which extend in the axial direction, are formed on respective surfaces or on a predetermined surface of the actuator body 3 for attaching the magnetism-detecting sensor 5. Each of the grooves 6 includes a circular groove 6a which has a substantially circular open cross section corresponding to the main body section 5a of the magnetism-detecting sensor 5, and a rectangular groove 6b which has a rectangular cross section, with one end communicating with the circular groove 6a and the other end being open to the outside.
However, in the case of the conventional technique as described above, the groove 6, which is formed on the surface of the actuator body 3, includes the circular groove 6a and the rectangular groove 6b corresponding to the shape of the magnetism-detecting sensor 5. The depth H of the groove 6 has a relatively large dimension extending inwardly from the contour surface of the actuator body 3. For this reason, the lateral dimension and the vertical dimension of the actuator body 3 are considerably large, due to the provision of the grooves 6. It is impossible to realize a compact size and a light weight of the overall actuator body 3.
Further, when the magnetism-detecting sensor 5 is installed to the actuator body 3, the following operation is required. That is, the magnetism-detecting sensor 5 is inserted into each of the grooves 6 from the end of the actuator body 3 (on the side of the rod 4), and then the magnetism-detecting sensor 5 is arranged at a predetermined position in the axial direction of the actuator body 3.
For this reason, it is necessary to use a relatively large space on the side of the rod 4 in order to attach and detach the magnetism-detecting sensor 5. It is difficult to effectively utilize a narrow space, and the operability to attach the magnetism-detecting sensor 5 is inferior.
A general object of the present invention is to provide a sensor attachment structure of an actuator body which effectively miniaturizes the actuator body with ease and which is excellent in operability to attach a sensor.
According to the present invention, a sensor is constructed to have a substantially rectangular cross section (thin shape), and the sensor is provided with a projection at an attachment end thereof, in which the projection protrudes outwardly. On the other hand, a sensor attachment groove, which has a substantially rectangular open cross section, is provided on a contour surface of an actuator body. The groove includes a tapered section which has widths gradually narrowed inwardly from the contour surface, and a spread section which is spread from narrow width ends of the tapered section and to which the projection of the sensor is installed.
Accordingly, the groove, which is provided on the contour surface of the actuator body, is designed to have a thin shape. It is possible to greatly reduce the dimension in the depth direction as compared with the conventional structure provided with the groove having the circular open cross section. Therefore, the contour dimension of the actuator body is effectively reduced. It is possible to realize a compact size and a light weight of the overall actuator body with ease.
When the sensor is attached to the groove, then the sensor is arranged at a predetermined position of the actuator body, and the sensor is pressed inwardly toward the groove. Accordingly, the sensor is easily inserted into the groove under the guiding action of the tapered section which constitutes the groove. When the projection of the sensor is installed to the spread section which is spread from the narrow width ends of the tapered section, then the sensor is reliably accommodated and secured in the groove, and thus the sensor is attached to the predetermined position of the actuator body. Accordingly, the operability to attach the sensor is effectively improved.
Further, when the sensor is composed of a flexible board which is formed to have a sheet-shaped configuration, a sensor attachment recess has an extremely minute depth. Alternatively, the sensor, which is composed of the flexible board having the sheet-shaped configuration as described above, may be directly stuck to an outer surface of an actuator body which is formed with no sensor attachment recess or the like at all, by using a sticking member.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.